1. Field of the Invention
The present invention relates to a display device.
2. Description of the Related Art
In recent years, along with an improvement of display performance of a liquid crystal display device, a display device is being actively used as an in-car display device. However, the in-car display device needs to cope with an environment for use of a car and to allow use under high temperature and low temperature, and is required to operate in a wide temperature range (use temperature range). Similarly, the in-car display device is required to have high vibration resistant performance so as to prevent looseness of assembly of components from occurring along with vibration of a car and the like.
As the technology of forming such a display device suitable for in-car use, for example, there is known the backlight unit described in JP 2008-27736 A. In the technology described in JP 2008-27736 A, the protrusions are formed on the inner side wall surfaces of the metal frame by molding a part of the metal frame serving as the case of the backlight unit. With this configuration, the light guide plate to be accommodated in the metal frame is fixed using elastic forces of the protrusions.
Further, the plurality of optical sheets such as diffusion sheets for uniformly diffusing the backlight emitted from the light guide plate are arranged on the light emitting surface side of the light guide plate. The optical sheets are generally fixed by being sandwiched between the light guide plate and the frame. As the technology of fixing the optical sheets, for example, there is known the liquid crystal display device described in JP 2002-72174 A. In the technology described in JP 2002-72174 A, the shaft provided with the protrusion is arranged on the short side of the frame made of plastics or metal, and the protrusion of the shaft is caused to pass through holes formed in the optical sheets, thereby fixing the optical sheets.
In addition, as illustrated in FIG. 18 and FIG. 19, there is known a configuration in which a plurality of rubber cushion members 2 are arranged between a light guide plate 1 and side walls of a lower frame 3 and between an optical sheet 4 and the side walls of the lower frame 3 to alleviate movement of the light guide plate 1 and the optical sheet 4 due to vibration by the rubber cushion members 2. In this configuration, the rubber cushion members 2 are fixed to three sides of the lower frame 3 excluding a side on the lower side of FIG. 18 or FIG. 19 at which a light source (not shown) is arranged.
In the technology described in JP 2008-27736 A, the light guide plate is pressed onto the side wall surfaces of the metal frame by spring elasticity of the protrusions, thereby holding the light guide plate. However, the light guide plate is formed of a transparent member made of an acrylic resin or the like, and hence there is a problem in that the light guide plate is chipped off because of rubbing between the end portion of the metal frame and the light guide plate due to vibration, and in a case where the chips enter the illumination surface illuminated with the backlight, a display quality of the liquid crystal display device is deteriorated. Further, when compared to the metal frame, the light guide plate made of a resin material has a larger coefficient of thermal expansion, and hence there is also a problem in that the light guide plate has a large amount of expansion particularly under high temperature and a large force is applied to the protrusions of the metal frame, thereby causing deformation of the light guide plate.
Further, in order to provide vibration resistant performance of the optical sheets using the technology described in JP 2002-72174 A, it is necessary to arrange the shafts at the opposed short sides of the frame, respectively, and to fix the optical sheets from both sides thereof using the two shafts. Meanwhile, the frame, which corresponds to a region surrounding the display region, does not contribute to image display, and hence is required to be narrowed. Thus, in the technology described in JP 2002-72174 A, the extended portion extended outward is formed at the center portion of the edge side on each side (short side) of the optical sheet, and the hole for allowing the protrusion of the shaft to pass therethrough is formed in the extended portion. Accordingly, in the technology described in JP 2002-72174 A, there is a fear in that the force applied to the optical sheets is concentrated on the extended portion, and because only the extended portion protrudes from the short side of the optical sheet, damage and wrinkles occur in the extended portion in a concentrated manner.
In addition, in the conventional configuration illustrated in FIG. 18 and FIG. 19, as illustrated in an enlarged view of FIG. 20, a clearance (gap formed considering expansion and contraction) corresponding to amounts of expansion and contraction of the light guide plate 1 and the optical sheet 4 due to temperature change is formed in advance. However, expansion coefficients of the optical sheet 4 and the light guide plate 1 made of a resin are approximately 4 to 6 times as large as that of the lower frame 3 or the like made of metal, and hence it is necessary to increase the clearance involved with temperature change in a longitudinal direction. Therefore, there is a fear in that backlash, damage, and the like accompanied with looseness and the like of the light guide plate 1 and the optical sheet 4 occur.